374 Proceedings of the Royal Society (f Edinburgh. 
Jan. 3. 1820. — Sir George Mackenzie, Bart., read a Paper, 
entitled, Speculations on the Nature of Sound. The facts 
which he chiefly dwelt upon were, first, That in every experi- 
ment, air has intervened between all bodies supposed to have 
the power of emitting and of conducting sound, and the appa- 
ratus of the ear ; % That sound varies in quality, and that the 
quality is not altered by transmission through different media, 
although the intensity of the sound may be increased or dimi- 
nished ; 3. That the intensity of sound does not depend on the 
rate of vibration ; 4. That different substances have the power 
of modifying the quality of sound ; 5. That there are cases in 
which sounds interfere with one another ; 6. That the same 
effect, in acquiring any pitch of sound, may be obtained by pre- 
serving a spring of the same length, while the volume of air 
connected with it is altered in dimension, (as in playing on a 
Jew’s harp) ; or by keeping the volume of air the. same, while 
the dimensions of the spring are altered, (as in the trumpet of 
an organ). Sir George Mackenzie’s opinions, as far as they were 
stated, are, 1. That sound is a medium sui generis ; 2. That this 
medium is emitted by no other substance but air ; 3. That it is 
not conducted through air, but that successive portions of air, 
when put into a certain condition by impulse, emit it ; and that 
when the impulse reaches the air in connection with the tympa- 
num, the sound emitted by that portion of air alone, is made per- 
ceptible to us by the apparatus of the internal ear ; and that we 
learn to judge of the distance of the body that gives the im- 
pulse, in a manner analogous to that by which we judge of the 
distance of objects in perspective ; and that our acquaintance 
with sounds, as they proceed from impulse given by certain 
means, is derived from an imperceptible induction, similar to 
that by which a child learns the meaning of words, and forms 
correct ideas of distance. Lastly, That all means of producing 
sound, are only means of causing air to emit it. 
Jan. 17. — Dr Fergusson, Inspector of Hospitals, read a pa^ 
per On the Nature and Properties of the Marsh Poison, as known 
under the titles of Marsh Miasmata and Malaria. The author 
endeavoured to prove, from a reference to the medical topo- 
graphy of various places in the South of Europe and the West 
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